Thoughts on Mortality

by Roger Bourke White Jr., copyright May 2010

Why do plants and animals -- and humans for those who hold that humanity is a special category -- age and die?

In some ways it seems like such a waste. We multi-cellular organisms go through all the trouble and hazard of getting born and growing up, why blow away all that hard-earned resource investment by getting old and dying?

The answer is that Mother Nature is still experimenting, and she has found that doing the experimenting is more successful than wiping her hands and saying, "I'm done, can't do any better than this." and making immortal beings. (Mother Nature is my anthropomorphizing of evolution and natural selection.)

There is one big reason why this continued experimenting is so valuable to do: Change. The conditions that organisms live in on earth are constantly changing, so experimenting stays valuable.

You may say, "The earth has been suitable for life for four billion years. What changes?"

The answer is many things on many time scales.

On the shorter time scale we have cyclic changes:

o changes between day and night

o changes in seasons

We also have random changes, which are better known as natural disasters:

o fires, floods, droughts, and many others

We have medium scale changes in the living community that surrounds us:

o diseases, new foods, new competitors, existing competitors evolving

And we have long time scale changes:

o migrations to new environments

o naturally occurring climate changes

o oceans rising and falling and continents drifting

o changes in the mixes of gases in the atmosphere and salts in the oceans

In sum, the world is a changing place and so it pays for Mother Nature to constantly run the experiment of, "Is this mix of organisms living in this particular place at this particular time the best I can do?"

Dying opens the way to running more experiments, and the aging process before death is not a random process, either, it's part of the experiment. One of the simplest indicators that aging is part of the experiment is the correlation between size and aging in mammals -- big mammals live longer. This happens because there is a correlation between the investment in growing to full size and how often the experiment of growing up should be done. If the organism takes a long time to grow up, then let the result last a long time... if it can. If it's a successful experiment, it will, and it will have grandchildren.

And having grandchildren is what it takes to pass Mother Nature's Test. If you are an organism that has lots of grandchildren you pass the test. If you don't... ah well.

And that's why we multi-cellular organisms of earth all live with aging and mortality. The Great Experiment is still going on.

Update: This 11 Jul 15 Science News article, Evolution may favor limited life span by Andrew Grant, covers this topic and comes to a similar conclusion: mortality is supported by evolution.